Devastating flash floods swept though numerous canyons along the Front Range of Colorado's Rocky Mountains Wednesday night and Thursday morning, washing out roads, collapsing houses, and killing at least two people. The floods were triggered by widespread torrential rains of 4 - 6" that fell in less than twelve hours, thanks to a flow of extremely moist air from the southeast that pushed up against the mountains. These sort of upslope rain events are so-named because as the air flows uphill, it expands and cools, forcing the moisture in it to fall as rain. Balloon soundings from Denver last night and this morning recorded the highest levels of September moisture on record for the station. The total precipitable water (PW), which is how much water would fall at the ground if the entire amount of water vapor through the depth of the atmosphere was condensed, was 1.33" at 12Z (8 am EDT) on September 12, and 1.31" at 00Z September 12. The previous September record was 1.23", set on September 10, 1980. Balloon soundings began in 1948. Wednesday night's rainfall was heaviest near Boulder, Colorado, where a flash flood watch continues through Thursday evening. Though rainfall amounts today are not expected to be as great as on Wednesday, the soils are saturated, and additional flash flooding will occur today as an upper-level low centered over the southern Great Basin continues to pull a moist southeasterly surface flow of air across Eastern Colorado. A map of Boulder flood zones and detailed history of previous floods in the area may be found here.

Dangerous 93L developing in the Gulf of MexicoA low pressure system (Invest 93L) over the Southwestern Gulf of Mexico's Bay of Campeche is generating heavy rains over the Yucatan Peninsula and adjacent waters as it moves west-northwest at about 5 mph. Radar loops from Mexico show that 93L has a pronounced rotation and is developing low-level spiral bands, and there is a strong possibility that the Air Force hurricane hunter plane scheduled to investigate 93L Thursday afternoon will find that a tropical depression has formed. Satellite loops show only a modest area of heavy thunderstorms, but these are steadily growing in intensity and areal coverage. The atmosphere is unusually moist, ocean temperatures are a very warm 29 - 29.5°C (84 - 85°F), and wind shear is a moderate 10 - 15 knots. These favorable conditions for development are expected to continue through Monday, according to the latest SHIPS model forecast. The computer models predict a landfall location along the Mexican coast between Veracruz and a location a few hundred miles south of the Texas/Mexico border by early next week. The storm is expected to maintain a forward speed of about 5 mph during the coming five days, and this slow motion will potentially allow 93L enough time to intensify into a hurricane before landfall. The high levels of moisture and slow motion of 93L make it a very dangerous rainfall threat, and I expect rainfall amounts of 5 - 10 inches will affect portions of the Mexican coast between Veracruz and Brownsville, Texas over the next five days. An added danger is the presence of tropical disturbance 90E in the Eastern Pacific Ocean, on the other side of Mexico. If 93L intensifies sufficiently, it could draw in the moisture from 90E across Southern Mexico, resulting in torrential rains on both the Pacific and Atlantic sides of Southern Mexico. In their 8 am EDT Thursday Tropical Weather Outlook, NHC gave 2-day odds of development of 60% and 5-day odds of 80%.

Figure 3. Latest satellite image of Tropical Depression Ten.

Humberto peaks in intensityHurricane Humberto is headed northwards over the far Eastern Atlantic, and has likely peaked in strength, with 85 mph winds. Humberto is listed in NHC's preliminary Best-Track data repository as having achieved hurricane strength at 8 am EDT on September 11, which would tie it with Hurricane Gustav of 2002 for latest appearance of the season's first hurricane since 1941. Satellite loops show that Humberto is well-organized hurricane with a distinct eye, but the storm has moved over waters cooler than 26°C, and wind shear has risen to 20 knots, which will likely cause weakening over the next few days. Humberto is not expected to be a threat to any land areas.

Gabrielle heads towards CanadaTropical Storm Gabrielle is headed northwards to Canada after bringing 40 mph winds and just over an inch of rain to Bermuda on Tuesday night. Satellite loops show that wind shear has ripped up Gabrielle, leaving the storm with almost no heavy thunderstorms, and exposing the low level circulation to view. Wind shear is expected to rise to an extremely high 45 - 70 knots on Friday as Gabrielle encounters a trough of low pressure, which will likely destroy the storm. Gabrielle's remnants will likely bring heavy rain to the Canadian Maritime Provinces on Friday and Saturday.

Quoting 1497. sar2401:No, flooding won't go on for weeks. As soon as it stops raining, the flooding will stop within 12 hours. The canyons that are flooding are the one too far down the mountain and have no flood control system. Most of this rain is being captured by large reservoirs further up in the mountains. This is, however, exactly the kind of rumor I wrote about in a previous post.

That is just not true. It takes time for the excess water to fully drain out of the mountains, hillsides, and groundwater, even if these are localized events. It may not take weeks, but it certainly wont be over in 12hrs. Many areas in Boulder are also inundated by several feet of water. That water wont just disappear, it will pond up and only gradually drain.

there is still a lot of water to come out of those mountains .. flooding will go on for weeks ..

No, flooding won't go on for weeks. As soon as it stops raining, the flooding will stop within 12 hours. The canyons that are flooding are the one too far down the mountain and have no flood control system. Most of this rain is being captured by large reservoirs further up in the mountains. This is, however, exactly the kind of rumor I wrote about in a previous post.

The rescuers I referenced earlier that are cut off, awaiting the National Guard, who in turn were (are?) cut off/stuck, are holding out in proceeding to Glendale due to that report about Lefthand. It's these unresolved situations that have me glued to the feed...

There are quite a few places that appear to be isolated and not reachable by emergency personnel at this time.

Listening to scanner is like a radio version of Twitter. A lot of information is passed along to emergency services by citizens, which has no way to confirm the traffic, so it gets posted in the command center and generally isn't acted upon until it's confirmed by a trained person with eyes on the situation or some official source, like a stream gauge or the USGS. Unfortunately, I was just looking at the scanner stream and there are almost 2,000 people listening, and a significant percentage are re-posting these unconfirmed reports to FB and Twitter. The media picks all this up and pretty soon, even the most outrageous rumors become true.

I wish these feeds didn't exist, because it's what's making many departments move to scrambling or unmonitorable radio systems. Boulder City and County have radio systems that any citizen in the local area can hear on $75 scanner. They are the ones that may be able use those scanner transmissions to help save their lives. Everyone else is listening because it's exciting or it's media, freelancers, and storm chasers getting information to advance their business interests or their hobby. Unfortunately, by the next time a disaster rolls around in Boulder, they may have a radio system no one can listen to, so we all lose, but especially the people who's lives and property is at risk.

Quoting 1488. sar2401:You have no idea how much I wish I could have been at that kayaker's take-out point so I personally could have hauled him off to jail. The entire area has already been declared a state and Federal disaster area, and all the local swiftwater resources are either in use or have been used up doing legitimate rescues. Now we have this nimrod decide to try some high-impact recreation, but he'd sure be screaming for us in emergency services to rescue his pasty white butt if he got into trouble. After 27 years in emergency services, risking my and my people's lives to save these type of narcissistic thrillseekers, you have no idea how cranked off this picture makes me.

Sar, on the sheriff/fire feed they just talked about some guys headed to high water w/ a 'green flotation device'...this is where the saying 'he ain't got the sense God gave a mule' can definitely apply.

I drive through that red triangle every day for work. I suspect the area will look a little different next time I see it...

This photo was taken earlier today on Boulder Creek near the left edge of the evacuation zone.

You have no idea how much I wish I could have been at that kayaker's take-out point so I personally could have hauled him off to jail. The entire area has already been declared a state and Federal disaster area, and all the local swiftwater resources are either in use or have been used up doing legitimate rescues. Now we have this nimrod decide to try some high-impact recreation, but he'd sure be screaming for us in emergency services to rescue his pasty white butt if he got into trouble. After 27 years in emergency services, risking my and my people's lives to save these type of narcissistic thrillseekers, you have no idea how cranked off this picture makes me.

Quoting MrMixon:The road closure report from cotrip.org looks like a joke. I haven't seen this many road closures since I've started using the site. Even winter storms don't shut down THIS many routes.

Had a brief lull (maybe 40 minutes), but rain is picking up again here...

Mr. Mixon, I'm glad to see you are OK and still "on the air", so to speak. I don't know what the ultimate solution to these kinds of issues is in the Boulder County area. As I'm sure you know, this is the largest flood in terms of area and possibly damage, but the Big Thompson Canyon Flood of 1976 killed 143, from similar causes, a large amount of rain over a fire burn area. Boulder County suffers from almost every kind of natural disaster there is, including floods, wildland fires, droughts, cold waves, heat waves, blizzards, severe thunderstorms, and tornadoes. Although it's not subject to hurricanes, it might as well be, given that Boulder County has been hit by hurricane force and above winds more frequently than any other place in the United States, including Gulf and East Coast states. Much of these flood waters and debris flows are coming down canyons that had almost no one living up them 75 years ago. Now, the city and country of Boulder have spread up these canyons to the point that places like Nederland and Lyon have become suburbs of Boulder, which is already a suburb of Denver. These types of disaster will only increase in the future, as people move into the mountains and alter the landscape. My son lived in Boulder for 10 years, and it's a beautiful area on a nice day. It's not so nice at times like this. :-(

All told, in NE Colorado and the immediate surrounding area, there are flash flood warnings currently in 15 counties in Colorado, 2 counties in Wyoming, and 2 counties in Kansas. The following NWS link shows this more clearly:

Not the entire city, but many intersections and roads are flooded and there is a surge of water reported to be headed towards Boulder. It remains to be seen how bad this surge or any subsequent surges might be. So far I think some buildings are flooded, but I don't think any buildings have "washed away" in Boulder (some have in Jamestown and other places).

Quoting 1469. MrMixon:Sheesh, now traffic on scanner is talking about a surge of water up to 7' deep coming down Lefthand Creek, with a possible breach in Lefthand Reservoir.

It's hard to say how accurate these reports are. I agree that a 30' surge on Four Mile Creek sounds a bit high. If that's accurate it would be exceptionally dangerous. We may not know for sure until it hits a gage... or town.

Gonna be hard to tear myself away from the scanner tonight...

The rescuers I referenced earlier that are cut off, awaiting the National Guard, who in turn were (are?) cut off/stuck, are holding out in proceeding to Glendale due to that report about Lefthand. It's these unresolved situations that have me glued to the feed...

There are quite a few places that appear to be isolated and not reachable by emergency personnel at this time.

...THIS IS A FLASH FLOOD EMERGENCY FOR BOULDER AND NORTHERNJEFFERSON COUNTIES ESPECIALLY FOURMILE CREEK AND BOULDERCANYON INTO THE CITY OF BOULDER...

AT 1131 PM MDT...LOCAL LAW ENFORCEMENT REPORTED SEVERE FLASHFLOODING ALONG FOURMILE CREEK. A VERY LARGE FLOW OF WATER WAS COMINGOUT OF EMERSON GULCH IN THE FOURMILE BURN AREA AND DOWN FOURMILECREEK. THIS WILL CAUSE ANOTHER SUDDED RISE IN FOURMILE CREEK ANDBOULDER CANYON OVER THE NEXT HOUR. LARGE AMOUNTS OF DEBRIS ANDVEHICLES WERE BEING CARRIED IN THIS FLOOD WAVE. WATER ALONG BOULDERCREEK IN THE CITY OF BOULDER WILL BE INCREASING THROUGH MIDNIGHT...AND THIS NEW FLOOD WAVE WILL LIKELY REACH BOULDER SHORTLY AFTERMIDNIGHT.

THE WATER CURRENTLY COMING INTO BOULDER WILL BRING EVEN HIGHER FLOWSTHAN THOSE CURRENTLY EXPERIENCED...WITH A WALL OF WATER POSSIBLE INBOULDER CANYON. IF YOU ARE NEAR BOULDER CREEK DO NOT TRY TOOUTRUN THE FLOOD WATERS...MOVE TO HIGHER GROUND NOW!

EXTENSIVE FLASH FLOODING ALSO CONTINUES ACROSS THE REMAINDER OFBOULDER AND NORTHERN JEFFERSON COUNTIES.

MOVE TO HIGHER GROUND NOW. THIS IS AN EXTREMELY DANGEROUS AND LIFETHREATENING SITUATION. DO NOT ATTEMPT TO TRAVEL UNLESS YOU AREFLEEING AN AREA SUBJECT TO FLOODING OR UNDER AN EVACUATION ORDER.

THIS IS A LIFE THREATENING SITUATION FOR PEOPLE ALONG BOULDER CREEKIN THE CITY OF BOULDER...IN THE FOURMILE BURN AREA...AND IN BOULDERCANYON. HEAVY RAINFALL WILL CAUSE EXTENSIVE AND SEVERE FLASHFLOODING OF CREEKS AND STREAMS FROM THE FOURMILE BURN AREA DOWNSTREAMTHROUGH THE CITY OF BOULDER. SOME DRAINAGE BASINS IMPACTED INCLUDEBOULDER CREEK...FOURMILE CREEK...GOLD RUN...FOURMILE CANYON CREEK...AND WONDERLAND CREEK. SEVERE DEBRIS FLOWS CAN ALSO BE ANTICIPATEDACROSS ROADS. ROADWAYS AND BRIDGES MAY BE WASHED AWAY IN PLACES. IFYOU ENCOUNTER FLOOD WATERS...CLIMB TO SAFETY.

BE ESPECIALLY CAUTIOUS AT NIGHT WHEN IT IS HARDER TO RECOGNIZE THEDANGERS OF FLOODING.

Sheesh, now traffic on scanner is talking about a surge of water up to 7' deep coming down Lefthand Creek, with a possible breach in Lefthand Reservoir.

It's hard to say how accurate these reports are. I agree that a 30' surge on Four Mile Creek sounds a bit high. If that's accurate it would be exceptionally dangerous. We may not know for sure until it hits a gage... or town.

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON HURRICANEHUMBERTO...LOCATED SEVERAL HUNDRED MILES NORTHWEST OF THE CAPEVERDE ISLANDS...TROPICAL STORM GABRIELLE...LOCATED A FEW HUNDREDMILES NORTHWEST OF BERMUDA...AND ON TROPICAL DEPRESSION TEN...LOCATED OVER THE SOUTHWESTERN GULF OF MEXICO.

AN AREA OF LOW PRESSURE LOCATED ABOUT 400 MILES EAST OF THE LEEWARDISLANDS IS PRODUCING LIMITED SHOWER AND THUNDERSTORM ACTIVITY.WHILE SURFACE PRESSURES ARE LOW IN THIS AREA...SIGNIFICANTDEVELOPMENT OF THIS SYSTEM IS UNLIKELY DUE TO UNFAVORABLEUPPER-LEVEL WINDS. THIS SYSTEM HAS A LOW CHANCE...10 PERCENT...OFBECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS...AND A LOWCHANCE...20 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THENEXT 5 DAYS WHILE IT MOVES TOWARD THE WEST-NORTHWEST AT ABOUT 10MPH.

A large surge of water, mud, rocks and debris, including cars, about 30 feet deep is heading down Fourmile Creek, according to an 11:10 p.m. call to Boulder County by a resident of Emerson Gulch. The flow is expected to reach Boulder Creek at about midnight.

Emerson Gulch is in the midst of the Fourmile Canyon fire burn area which was denuded of grass, trees and brush.

Hope that resident is exaggerating that figure, was just about to post that. Stay safe Mr Mixon. The area around Table Mesa in Boulder I recently moved from looks pretty bad.

I have been listening to the scanner. It takes a special kind of person to run dispatch.

Surprisingly, we still have power. We're southeast of Nederland and technically are on a different power grid than town. I noticed at least one new tree down in our woods and I imagine a few more will come down around the county before this is over with these saturated soils.

May not post much more tonight, but mainly because I'm getting tired. Will check in as I can. Fingers crossed for the power to hold out...

Our thoughts are with you and everyone in 'harm's way' tonight. Hope you get some good rest.

A large surge of water, mud, rocks and debris, including cars, about 30 feet deep is heading down Fourmile Creek, according to an 11:10 p.m. call to Boulder County by a resident of Emerson Gulch. The flow is expected to reach Boulder Creek at about midnight.

Emerson Gulch is in the midst of the Fourmile Canyon fire burn area which was denuded of grass, trees and brush.

A large surge of water, mud, rocks and debris, including cars, about 30 feet deep is heading down Fourmile Creek, according to an 11:10 p.m. call to Boulder County by a resident of Emerson Gulch. The flow is expected to reach Boulder Creek at about midnight.

Emerson Gulch is in the midst of the Fourmile Canyon fire burn area which was denuded of grass, trees and brush.

Are you listening to the sheriff/fire audio feed? It's never-ending...I can't make myself turn it off. Waiting to hear about the rescuers who are cut off, who are waiting on the National Guard, who themselves are stuck. The dispatchers, though, I don't know how they keep it all straight. One of them has been on literally all day and tonight.

I have been listening to the scanner. It takes a special kind of person to run dispatch.

Quoting 1442. LAbonbon:

From the feed: Power lost in Nederland, where I think MrMixon lives (can anyone confirm?), so we may not be hearing from him even after he rests. Hope all is well w/ him.

Surprisingly, we still have power. We're southeast of Nederland and technically are on a different power grid than town. I noticed at least one new tree down in our woods and I imagine a few more will come down around the county before this is over with these saturated soils.

May not post much more tonight, but mainly because I'm getting tired. Will check in as I can. Fingers crossed for the power to hold out...

Quoting 1448. TropicalAnalystwx13:If you read back you will notice that I did not quote Stormchaser121.

You quoted scott, but I took his comment to mean, in what was an ongoing discussion about the ensemble system between me and Stormchaser, that he was talking about the latter system, not 10L. I could have interpreted that wrong though, but that's the kind of context I would have gotten given the situation.